Alkane bis-dichlorophosphines are known compounds (see: Zur Spaltung tertiarer Phosphine, K. Sommer, Zeitschrift fur anorganische und allgemeine Chemie, Band 376, pp. 37-43, 1970). These compounds are prepared by reacting a 1,2 ethyl bis-diphenyl phosphine with phosphorus trichloride in the presence of an aluminum chloride catalyst for 5 hours at 280.degree.C. in a heated autoclave as per the following reaction: EQU .phi..sub.2 PCH.sub.2 CH.sub.2 P.phi..sub.2 + 4PCl.sub.3 .fwdarw. Cl.sub.2 PCH.sub.2 CH.sub.2 PCl.sub.2 + 4.phi.PCl.sub.2
The yield is approximately 60%. However, this reaction requires a complex starting material which is difficult to prepare, and the 60% yield does not reflect losses in the preparation of the starting material. Also, this reaction requires high temperatures. Any reduction in the temperature would provide a definite cost and energy saving.
It is well known that phosphorus trihalide is an effective free radical scavenger. It is also known that phosphorus trihalide will react with olefins or ethylenically unsaturated compounds, generally in the presence of a catalyst to form monophosphine compounds (see: Radiation-induced Synthesis of Organophosphorus compounds, II. Products of Radiation-induced Synthesis from Mixtures of Olefins and Phosphorus trichloride, E. I. Babkina and I. V. Vereshchinskir, L. Ya., Zhurnal Obshchei Khimii, Vol. 41, No. 6, pp. 1248-1253, June, 1971; The Phosphorus Trichloride-Oxygen-Olefin Reaction: Scope and Mechanism, C. B. C. Boyce, S. B. Webb & L. Phillips, Journal Chemical Society, 1974, pp. 1650-1658; Radiation Induced Synthesis of Organophosphorus Compounds, Products of Radiation-induced Synthesis from Mixture of Hydrocarbons and Phosphorus Trichloride, E. I. Babkina and I. V. Vereshchinskii, Zhurnal Obshchei Khimii, Vol. 41, No. 8, pp. 1772-1776, August, 1968; A New Method of Preparation for Alkenylphosphonous Dichlorides and Alkenylthiophosphonic Dichlorides, Walsh, Beck and Woodstock, Journal of the American Chemical Society, 77, 929 (1955) (elemental phosphorus and iodine are used in a reaction with PCl.sub.5 and an olefin to produce alkenyl phosphonous dichlorides); Photochemical Initiation of Radical-Chain Addition of Phosphorus Trichloride to Olefins, J. R. Little and P. F. Hartman, Journal of the American Chemical Society, 88, pp. 96 - 100, January 5, 1966; Addition of Phosphorus Trihalides to Olefins, B. Fontal and H. Goldwhite, Journal of Organic Chemistry, 31, pp. 3804-3806 (1966); C. Walling and M. S. Perason, Topics in Phosphorus Chemistry, Vol. 3, p. 11 E. J. Griffith and M. Grayson, Editors, Interscience, N.Y., 1966; New Reaction for the Production of Beta-chloroalkyldichlorophosphines from Olefins According to an Ionic Mechanism, A. I. Titov, M. V. Sizova, and P. O. Gitel, Doklady Akademii Nauk, S.S.S.R., Vol. 159, No. 2, pp. 385-388, November, 1964; U.S. Pat. Nos. 2,489,091, 2,510,699, 2,671,077, 2,671,078, 2,671,079, 2,671,080; Preparation of Long-chain Alkenylphosphonates, Nitta, Okamoto & Sakural, Yukagaku, 1969 18(10), 747-750 (Japan); Mechanism of Radical Chain Addition Reaction Termination for Phosphorus Trichloride Addition to Olefins, Shostenko, Zagoreta, Dadonov, Greish, Tr. Mesh Khim Tekhmd Inst., 1969, No. 62 100-103). All of these references basically relate to the reaction of an olefin with PCl.sub.3 to form a RPCl.sub.2 compound. Dihalophosphines are not contemplated nor formed by these reactions.
Applicants' co-pending application, Ser. No. 151,955, filed June 10, 1971, teaches that bis-phosphonic and phosphinic halides and their sulfur analogs can be prepared by reacting an olefin such as ethylene, propylene and butylene with a trivalent phosphorus comound in the presence of P.sub.4 O.sub.10 or P.sub.4 S.sub.10 (the latter for the sulfur analogs) under at least autogenous pressure at a temperature of from 200.degree.C. to 450.degree.C. The compounds prepared by this method are pentavalent phosphorus compounds. Trivalent alkane bis-dihalophosphines cannot be prepared by this method.
It is also known that alkyl- or arylphosphonous dichlorides can be prepared from an alkyl or aryl halide, phosphorus trichloride and phosphorus at elevated temperatures in an autoclave at autogenous pressure (A Direct Synthesis of Alkyl (or Aryl) Dichloro- and Dibromophosphines, N. K. Bliznyuk, Z. N. Kvasha & A. F. Kolomiets, Zhurnal Obshchei Khimii, Vol. 37, No. 4, pp. 890-892, April, 1967). This method, however, cannot be used for the preparation of the alkane -bis-dihalophosphines.